A review on the experimental non-intrusive investigation of fuel injector phase changing flow

Two-phase in-nozzle flows, such as cavitation and flash boiling, have been well studied as effective means to enhance spray breakup and atomization via phase change both within the nozzle and outside the nozzle. However, the challenges in observing the transient and complex phase change phenomena for such sprays have prevented further insights into the physics behind. The analysis and investigation on multiphase flow inside an atomizing nozzle are significant to elucidate the physics of liquid breakup mechanism and spray evaporation phenomenon. As such, optical accessible injectors and corresponding non-intrusive measurement techniques have been utilized in recent years to thoroughly investigate the multiphase flow characteristics within the nozzle. This work presents a comprehensive review of recent experimental efforts on using optical diagnostics and/or transparent nozzles. Aspects such as typical experimental apparatus, multiphase flow characteristics, measurement capacities and limitations, etc. are presented and discussed. The advantages/drawbacks of each technique are also incorporated. Finally, this review article comments on future opportunities and challenges of non-intrusive investigations for two-phase in-nozzle flows in obtaining better spray atomization performance.